The present invention generally relates to an implantable device or appliance having a surface which has a porous structure, the porous structure being of the type that enhances organic tissue ingrowth thereinto when the device or appliance is implanted. More particularly, the invention relates to implantable devices or appliances and to a method for producing same, such including an electrically conductive porous coating of plasma deposited elemental metal particles laid down by pressure spraying a gaseous composition onto a surface of the device, the gaseous composition including molten elemental metal powder or particles in an atmosphere of reductive gases in order to provide an environment which substantially eliminates oxidation of the metal particles in order to thereby avoid the need for subsequent treatment to remove metal oxides.
It has been recognized that in many medical applications, it is desirable to provide a tissue-compatible porous surface. The porous nature of such a surface allows tissue to grow into the porous surface in order to more effectively implant or incorporate the device or appliance into the body. Such ingrowth assists in holding the device in place within the body. Over the years, various approaches have been taken in an effort to provide tissue-compatible porous surfaces that are implantable and that promote tissue ingrowth.
Many of these prior approaches involve sintering of particles in order to form the particles into a porous network having a porosity that is suitable for promoting tissue ingrowth. Generally speaking, such sintering approaches are quite successful in providing the type of porous surface that is desired. Exemplary patents in this regard include U.S. Pat. Nos. 4,101,984 and 4,280,514. A typical sintering procedure includes forming a self-supporting coating of metallic particles which are bound to one another and to the underlying substrate by an adhesive material. Thereafter, the adhesive material or binder is dried in order to provide a preform of dried coating on the substrate, which preform is thereafter sintered to thereby bring about metal fusion of generally adjacent metal particles in order to interconnect the metal particles with one another and with the underlying metal substrate. The presintering self-supporting preform or coating of metal particles and adhesive material or binder are prepared by various procedures. For example, the metal particles may be mixed with the binder or adhesive material into a slurry which is sprayed onto the substrate or within which the substrate is dipped.
In these types of procedures, time must be taken in order to dry the substrate, binder and metal particles preform. Preform or presintering temperatures for effecting the drying require raising the materials to an elevated temperature, and the sintering procedure also requires raising the materials to an elevated temperature. Typically, presintering and sintering temperatures vary depending somewhat upon the particle size, temperature ranges in this regard being between about 2,000.degree. F. and about 2300.degree. F., that is between about 1,100.degree. C. and about 1,250.degree. C., for relatively long periods of time, usually between about 90 and 180 minutes. Also, when it is desired to provide sintered porous surface products that are of especially superior quality, it is desirable that the metallic particles be as spherical as possible and exhibit a narrow particle size distribution. Also, the self-supporting coating must be carefully prepared prior to sintering, and it should be fixtured within the furnace, which requirements interfere with the suitability of sintering procedures for use in mass production operations.
Materials out of which these porous surface coatings have been made include porous platinum surfaces and less expensive high technology alloys, as well as carbon. Included has been the utilization of a porous carbon layer over a surface of a shaped, implantable device, appliance or implement. Typically, such porous carbon layers are laid down by sintering or other procedures that include subjecting the surfaces to high temperatures, which often results in the formation of a pyrolytic carbon coating that is vitreous or glassy and somewhat amorphous. Additionally, when carbon is laid down by a procedure such as sintering, the characteristics of sintering prevail, that is the carbon is coated in bulk quantities first, after which it is sintered under harsh treatment conditions which, for carbon, can result in a final product that is of reduced stability and uniformity.
It would accordingly be desirable to provide implantable devices which have highly electrically conductive surfaces that are of a porous nature in order to promote tissue ingrowth, which surfaces are prepared by a procedure other than sintering. Such most advantageously should lend itself to mass production by providing the porous coating without having to undergo extensive fixturing, and same should not require heating the device to high temperatures. It would also be desirable if especially superior products could be provided without having to utilize particles that are substantially spherical and/or that fall within a narrow size distribution range.
These various properties, needs and objectives are achieved by the present invention, by which a porous implantable device is provided without sintering. A supply of elemental metal powder flows with a supply of reductive gas past a power source in order to plasma deposit the elemental metal in a manner that achieves the desired porosity. The elemental metal particles are electrically conductive. After treatment in accordance with this invention, they retain their electrical conductivity without further treatment since there is no significant formation of metal oxides on the metal particles, due principally to the reductive nature of the plasma gas environment. Requiring spherical powder particles and high temperature heating of the device or implement are avoided according to the present invention, which is well suited for mass production manufacturing procedures.
It is accordingly a general object of the present invention to provide an improved implantable device including a plasma deposited porous layer.
Another object of the present invention is to provide an implantable device having a porous surface that is formed from elemental metallic particles that are pressurized and plasma deposited while avoiding oxide formation.
Another object of the present invention is to provide an improved porous-surfaced device or implement that lends itself well to being manufactured on a mass production scale.
Another object of this invention is to provide an improved implantable device or appliance that promotes colonization and tissue ingrowth into the depth of the porous surface from adjacent body tissue within which it is implanted in order to provide bonding between the body tissue host and the porous member.
Another object of this invention is to provide an implantable device having a porous surface, which device is manufactured without having to raise its temperature to a substantially high level.
Another object of the present invention is to provide an improved device and process which utilizes plasma deposition techniques for the formation of a porous implantable coating having high electrical conductivity.
These and other objects, features and advantages of this invention will be clearly understood through a consideration of the following detailed description.